Bernard D. Zetler

MODE Bottom Experiment

Abstract Pressure fluctuations on the deep seafloor at frequencies below inertial and tidal have been measured. Between 0.1 and 1 cycle per day the variance is about 2 mb2, spectra diminish with increasing frequency as ω−n, n=1.5 to 2, and a signal-to-instrument noise ratio of 10 dB is achieved. Fluctuations are in phase and highly coherent within the MODE area (>0.95 at 200 km) and even with inferred (atmosphere plus sea level) Bermuda subsurface pressures (0.8 at 700 km). Station differences (to which MODE-sized eddies would make the principal contribution) are relatively small. The large horizontal scale of the recorded bottom pressure fluctuations resembles that of atmospheric pressure, yet the coherence locally between atmospheric and bottom pressure is slight; the recorded fluctuations may be related to a barotropic ocean response to a variable wind stress on the subtropical gyre. Bottom temperature records show “sudden” (1 day) changes of order 30 millidegrees Celcius separated by long intervals (2...

Radiational Ocean Tides Along the Coasts of the United States

Abstract A procedure has been developed for separating an analyzed S2 ocean tide amplitude and phase into gravitational and radiational components. Values obtained by applying the method to 11 one-year sets of harmonic constants at San Francisco were found to be reasonably consistent. Results have been obtained for 15 outside or near-outside stations on each of the east and west coasts of the United States. For both coasts the mean amplitude ratio (radiational to gravitational) is 0.16; the mean phase differences (radiational minus gravitational) are 133° and 185° for west and east coasts, respectively. The observed S1 amplitude of 1 cm, consistent on the east, west and Gulf coasts, is larger than would he expected from equilibrium considerations, from the K1 cusp, or from the continuum; it is therefore considered to be primarily radiational.

Interpretation of multipath scintillations Eleuthera to Bermuda in terms of internal waves and tides

Rate‐of‐phase and intensity spectra due to time‐varying multipath interference depend essentially on a single parameter ν2 which can be interpreted as the mean‐square rate‐of‐phase for any typical single path. MIMI 406‐Hz phase and intensities are consistent with ν−1=270 and 357 sec for Eleuthera to Bermuda and Eleuthera to midstation transmissions, respectively, compared to 192 and 286 sec from a ray‐geometric calculation using an internal wave model based on oceanographic observations. Internal tides play a significant but not dominant role.Subject Classification: [43]30.20, [43]30.35.

Predicted Extreme High Tides for Mixed-Tide Regimes

Abstract There are a number of published studies of the astronomical conditions prevailing when extreme high tides are predicted, but usually these are directed toward tidal regimes that are dominantly semidiurnal. The published criteria are found to be inadequate for mixed regimes (diurnal tides roughly the same order of magnitude as the semidiurnal tides in the area). For the mixed tides on the California coast, added consideration must be given to tropic tides (diurnal tides larger than average when the moon is near maximum declination) and to the 18.61-year period of the lunar-node cycle. Furthermore, extreme high diurnal tides tend to occur when the sun is near maximum declination (summer and winter) whereas comparable semidiurnal tides ordinarily occur near the equinoxes (spring and fall). Because of these added complications, harmonic tide predictions were prepared for four California ports up to the year 2000 so that information on extreme high tides could be tabulated. These data help to alleviat...

Tidal observations near an amphidrome

The signal to noise ratio in tidal data in the diurnal and semidiurnal frequency bands is ordinarily so large that the noise contribution to the tidal harmonic constants is unimportant. However, as the observational locations are selected progressively closer to an amphidrome (point of no tide), the signal to noise ratio decreases, making the tidal harmonic constants less dependable. Standard deviations in amplitude of M2 and S2 obtained from 12 29-day analyses of a year of tide data obtained at a standard tide station, estimated to be 280 and 550 km away from the amphidromes for these constituents in the eastern Caribbean, are roughly one-third of the mean amplitudes for these constituents; the standard deviations in epoch are 38° and 30° respectively. Therefore, a program to locate an amphidrome precisely is self-defeating and the location can only be approximated by a grid of tide observations spanning the geographic position and/or by longer series of observations, using higher resolution to increase the signal to noise ratio. Amplitudes of 0.64 cm and 1.24 cm were calculated for M2 and S2 from a one-month series of pelagic observations obtained very close to an inferred position of the M2 amphidrome in the northeast Caribbean Sea.

IAPSO compilation of pelagic tides

The harmonic method of analyzing and predicting tides was an outstanding scientific accomplishment in the nineteenth century. Except for the building of bigger and better mechanical tide‐predicting machines, procedures were essentially unchanged during the first half of the twentieth century. Cotidal and co‐range charts were empirical, based on observed tides along coastlines and at a few islands. More recently, numerical solutions of Laplace tidal equations have become feasible on newlydeveloped, more powerful computers. Simultaneously, oceanographic engineers have succeeded in measuring tides on the sea floor at great depths. To make pelagic tide data available to the oceanographic community, in particular to those involved in tidal modeling, the IAPSO Advisory Committee on Tides and Mean Sea Level has published a compilation of pelagic tides. The first edition, published in 1979, has harmonic constants for 108 stations, each at least 100 m deep and one nautical mile offshore.

Tides at Port Mansfield, Laguna Madre, Texas

Abstract The tides at Port Mansfield are so small (mean diurnal range of about 2 cm) that they are nearly lost in a noisy (meteorological) continuum. Nevertheless, a precise tidal analysis is necessary to provide the data for a determination of the elevation of mean high water, the boundary between private and state ownership in an oil‐producing area with a very flat terrain. Although response tidal analysis has been shown to be somewhat superior to classical harmonic analysis in various previous tests, no advantage is found in these circumstances of extremely low sighal‐to‐noise ratio.